Due to the Internet's sheer size, complexity, and various routing policies, it is difficult if not impossible to locate the causes of large volumes of BGP update messages that occur from time to time. To provide dependable global data delivery we need diagnostic tools that can pinpoint the exact connectivity changes. We describe an algorithm, called MVSChange that can pin down the origin of routing changes due to any single link failure or link restoration. Using a simplified model of BGP, called simple path vector protocol (SPVP), and a graph model of the Internet, MVSChange takes as input the SPVP update messages collected from multiple vantage points and accurately locates the link that initiated the routing changes. We provide theoretical proof for the correctness of the design.